Re: Math expression evaluation error?

[Peter Stephenson <p.w.stephenson@xxxxxxxxxxxx>]

On Fri, 09 Jan 2015 13:40:42 -0800
jdh <dhenman@xxxxxxxxx> wrote:
> Thanks for the detailed explanation.   I suggest that the an additional 
> line be added to the manual, which would say something like:
> 
> "   Caution:  The evaluation of an expression is taken a term at a time 
> and if there are mixed terms , say integer only and  float terms , the 
> integer only ones will not be promoted to real values and the result of 
> the whole expression would be an error to common standards. One can use 
> the -f option or the  FORCE_FLOAT environment variable to change this 
> behavior."

Thanks, that's just the sort of useful feedback on what people find
confusing that we need.  I've adapted it into the appropriate section of
the manual with minor corrections.

diff --git a/Doc/Zsh/arith.yo b/Doc/Zsh/arith.yo
index a620b73..5c334ce 100644
--- a/Doc/Zsh/arith.yo
+++ b/Doc/Zsh/arith.yo
@@ -233,6 +233,15 @@ necessary.  In addition, if any operator which requires an integer
 equivalents with assignment) is given a floating point argument, it will be
 silently rounded down to the next integer.
 
+Users should beware that, in common with many other programming
+languages but not software designed for calculation, the evaluation of
+an expression in zsh is taken a term at a time and promotion of integers
+to floating point does not occur in terms only containing integers.  A
+typical result of this is that a division such as tt(6/8) is truncated,
+in this being rounded down to 0.  The tt(FORCE_FLOAT) shell option can
+be used in scripts or functions where floating point evaluation is
+required throughout.
+
 Scalar variables can hold integer or floating point values at different
 times; there is no memory of the numeric type in this case.
 
 
pws